As impressive as Sea of Thieves may have been from a graphical standpoint, there wasn't much of a reason for people to play the game given its lack of content. Thankfully, Rare seems to be aware of one of the most common complaints about Sea of Thieves and unveiled a general roadmap of what players can expect over the coming months, presumably in an attempt to assuage people's fears that the game is going to be abandoned or somesuch. In short, you can expect more places to explore, more enemies to kill, and more gameplay mechanics to come to the game over the next couple of months.
In May, there will be a major update called The Hungering Deep that will bring a "new AI threat to the world." Crews (meaning multiple ships/parties) will have to work together to discover and defeat this threat in an event that will feature unique mechanics and rewards.
In the summer, another major update, Cursed Sails, will introduce a new ship type to Sea of Thieves. Like Hungering Deep, Cursed Sails will also have its own end-game boss of a sort, but the main draw of Cursed Sails will be the expanded variety of ships that you can encounter from both a functional and cosmetic standpoint.
Forsaken Shores is the last, and perhaps most ambitious, named content update for Sea of Thieves. In addition to a new area to explore, Forsaken Shores will introduce new gameplay mechanics, new enemies to fight, and new rewards to claim that are "themed to that part of the world."
In the fall and winter, there will be three more major updates for Sea of Thieves, but the nature of these updates have yet to be revealed.
In between all of these aforementioned major updates, weekly events will be introduced into the game as a means for players familiarize themselves with things like new mechanics and locations, or to encourage people to explore existing content. Such weekly events can be as simple as new trading company missions or helping an NPC recover a chest from a location that you would have no reason to explore otherwise. However, these weekly events can also be used to let players experiment with things like cursed cannonballs or some other new items that can create more conflict or cooperation between different crews.
Fortunately, all major content updates will be available for free, and their associated enemies, mechanics, etc. will be integrated into the Sea of Thieves world for anyone to stumble upon whenever they want. This also means that, with these new content updates, Rare will be putting Pets and Ship Captaincy on hold until things settle down.
It should be noted that Rare is being very vague about the nature of these new content updates for Sea of Thieves, likely because they want to give themselves some leeway in the event that plans change. To their credit though, Rare is reacting in a swift and reasonable manner to criticism (which is never a bad thing), and their planned content updates appear to be quite fair, at least on paper. The real question is whether or not it will be enough to keep people interested in Sea of Thieves over the next couple of months as such promises have been made before by other developers to mixed results.